This project aims to characterize human motion perception as mediated by vision, vestibular system, and the interactions between them. The project is divided into 3 main areas: vestibular perception, visual-vestibular interaction, and visual motion perception. The vestibular perception component will focus on determination of translation, heading perception, and rotation in normal controls and individuals with unilateral and bilateral peripheral vestibular lesions in the absence of visual cues. Differences in these populations may provide better understanding of vestibular sensitivity, including potential direction biases in sensitivity in those with unilateral lesions and form the basis of future diagnostic testing. Subjects with bilateral vestibular loss may provide clues to the roll of somatic sensation on motion perception. Vision has a significant role in motion perception, and patient's dizziness symptoms can result from derangements in integration of vision and vestibular cues. The most simple interaction between visual and vestibular perception occurs during rotation near the perceptual threshold in the presence of a visible, head fixed object. Paradoxically, in this situation a visible object has been shown to decrease the motion perception threshold. We plan to study this effect with moving objects and in individuals with known pathology in the visual-vestibular integration system such as occurs in migraine associated vertigo (MAV). Using this paradigm we also plan to explore perceptual differences between self and external rotation. We also plan to study the roles visual-vestibular interaction during translation using optic flow with motion to determine heading perception, in normal controls, MAV, and vestibulopathy subjects. Through these experiments we hope to quantify the influences of vision and vestibular senses on motion perception, and how the relative importance of these influences changes in pathological states. Many prior perceptual studies have used 2-alterative forced choice (2AFC) paradigms which are scientifically rigorous, but time consuming. Potential short cuts 2AFC that will speed testing and allow possible clinical applications will be explored. Dizziness in response to visual motion such as panning of the scene on a movie screen or looking out the side window of a moving vehicle is a disorienting source of dizziness complaints in MAV patients which often limits their daily activities. We plan to investigate the potential for visual motion as a diagnostic and rehabilitation strategy in these subjects. Using a specially developed web-based application, control and MAV subjects will complete a subjective visual vertical (SVV) task. The effect of background motion will be determined as well as tolerance to the stimuli. Subjects will regularly use the application over time while periodically reporting their dizziness symptoms using validated clinical instruments. The potential diagnostic value of the task, its correlation with symptom severity, and potential as a rehabilitation strategy will be investigated.